The present invention is directed to electrical circuits known as closed-loop circuits. By way of example and not by way of limitation, a common-mode feedback loop is described herein as an exemplary embodiment of such a closed-loop circuit. One skilled in the art will easily recognize that the method and apparatus of the present invention may be advantageously employed with other closed-loop circuits.
A critical design consideration of closed-loop circuits is to ensure that the circuits are stable. A common criterion of stability is to design a loop so that its open loop phase margin is sufficiently large. A typical such design consideration is to ensure that open loop phase margin is  greater than 45xc2x0. It is particularly desirable to have open loop phase margin be in the range of 60xc2x0-90xc2x0.
Phase margin ("PHgr"M) is inversely proportional to loop bandwidth (LBW). Settling time TS of a loop circuit is also inversely proportional to LBW. Thus, there is a trade off between "PHgr"M and TS. A smaller LBW gives a higher "PHgr"M at the expense of a longer TS. A larger LBW may also be established with a shorter TS, but with a lesser "PHgr"M.
There is a need for a method and apparatus for affecting speed of transition of a closed loop circuit from an initial state to a steady state that improves settling time TS while maintaining phase margin "PHgr"M at an acceptable value.
A method for affecting speed of transition of a closed loop circuit from an initial state to a steady state during a transition period; the closed loop circuit including a switching unit effecting the transition in response to a gating signal applied to a gate locus at a value greater than a predetermined threshold potential; includes the steps of: (a) at least one of: (1) clamping the gate locus at a minimum potential greater than ground potential and less than the predetermined threshold potential; and (2) increasing potential at the gate locus at a plurality of various rates during a plurality of segments of the transition period.
An apparatus for affecting speed of transition of a closed loop circuit from an initial state to a steady state during a transition period; the closed loop circuit including a switching unit effecting the transition in response to a gating signal applied to a gate locus at a value greater than a predetermined threshold potential; comprises: (a) at least one of: (1) a clamping means coupled with the gate locus for clamping the gate locus at a minimum potential greater than ground potential and less than the predetermined threshold potential; and (2) a potential controlling means coupled with the gate locus for increasing potential at the gate locus at a plurality of various rates during a plurality of segments of the transition period.
It is, therefore, an object of the present invention to provide a method and apparatus for affecting speed of transition of a closed loop circuit from an initial state to a steady state that improves settling time TS while maintaining phase margin "PHgr"M at an acceptable value.